Myanmar has been in turmoil since Aung San Suu Kyi's civilian government was toppled in an army coup almost two years ago.

Long-established ethnic rebel groups, as well as dozens of "People's Defence Forces" (PDF), have emerged in opposition and clash frequently with the military.

The last few days have seen intense clashes in southeast Karen state, around Kyonedoe and the border town of Payathonzu.

"There were drone attacks by local PDFs at a military command near Kyonedoe town a few days ago," a military source told AFP.

"Nearby military released sporadic artillery fire at the PDF locations to warn them," the source said, without elaborating.

Residents of Kyonedoe, which has a population of around 5,000, said they endured a tit-for-tat battle as the rebels shot back.

"There was shooting the whole night. We dare not to stay. It was so frightening," said one resident, who requested anonymity.

"Thousands of residents have been fleeing the town as well as nearby villages," the resident added.

It comes as Karen armed forces attacked Payathonzu, around 180 km (110 miles) to the south, on the Thai border on Monday night.

They burned down several government departments including the immigration, military intelligence and administration bureaus.

"They shot into the town for half an hour, then burnt down those offices," said one resident, who asked to remain anonymous and added he had moved his family to the Thai side for safety.

Another resident, who also requested anonymity, estimated that as many as a thousand people had fled.

"We heard that the Thais opened the border for only half a day, but they kept the border open as more and more people keep crossing," he said.

A Thai army spokesperson did not respond to request for comment.

More than 2,700 civilians have been killed since the military grabbed power in February 2021, according to a local monitoring group.

The junta blames anti-coup fighters for a civilian death toll it has put at almost 3,900.